Re: [PATCH] s390: protvirt: virtio: Refuse device without IOMMU

[Pierre Morel]

On 2020-06-15 05:01, Jason Wang wrote:
> On 2020/6/12 äå7:38, Pierre Morel wrote:
> > On 2020-06-12 11:21, Pierre Morel wrote:
> > > On 2020-06-11 05:10, Jason Wang wrote:
> > > > On 2020/6/10 äå9:11, Pierre Morel wrote:
> > > > > Protected Virtualisation protects the memory of the guest and
> > > > > do not allow a the host to access all of its memory.
> > > > >
> > > > > Let's refuse a VIRTIO device which does not use IOMMU
> > > > > protected access.
> > > > >
> > > > > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > > > > ---
> > > > > Â drivers/s390/virtio/virtio_ccw.c | 5 +++++
> > > > > Â 1 file changed, 5 insertions(+)
> > > > >
> > > > > diff --git a/drivers/s390/virtio/virtio_ccw.c 
> > > > > b/drivers/s390/virtio/virtio_ccw.c
> > > > > index 5730572b52cd..06ffbc96587a 100644
> > > > > --- a/drivers/s390/virtio/virtio_ccw.c
> > > > > +++ b/drivers/s390/virtio/virtio_ccw.c
> > > > > @@ -986,6 +986,11 @@ static void virtio_ccw_set_status(struct 
> > > > > virtio_device *vdev, u8 status)
> > > > > ÂÂÂÂÂ if (!ccw)
> > > > > ÂÂÂÂÂÂÂÂÂ return;
> > > > > +ÂÂÂ /* Protected Virtualisation guest needs IOMMU */
> > > > > +ÂÂÂ if (is_prot_virt_guest() &&
> > > > > +ÂÂÂÂÂÂÂ !__virtio_test_bit(vdev, VIRTIO_F_IOMMU_PLATFORM))
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂ status &= ~VIRTIO_CONFIG_S_FEATURES_OK;
> > > > > +
> > > > > ÂÂÂÂÂ /* Write the status to the host. */
> > > > > ÂÂÂÂÂ vcdev->dma_area->status = status;
> > > > > ÂÂÂÂÂ ccw->cmd_code = CCW_CMD_WRITE_STATUS;
> > > >
> > > >
> > > > I wonder whether we need move it to virtio core instead of ccw.
> > > >
> > > > I think the other memory protection technologies may suffer from 
> > > > this as well.
> > > >
> > > > Thanks
> > >
> > >
> > > What would you think of the following, also taking into account 
> > > Connie's comment on where the test should be done:
> > >
> > > - declare a weak function in virtio.c code, returning that memory 
> > > protection is not in use.
> > >
> > > - overwrite the function in the arch code
> > >
> > > - call this function inside core virtio_finalize_features() and if 
> > > required fail if the device don't have VIRTIO_F_IOMMU_PLATFORM.
>
>
> I think this is fine.

Thanks,
I try this.

Regards,
Pierre




--
Pierre Morel
IBM Lab Boeblingen